The present invention relates to an apparatus and a method for determining the drying time of a piece of wood among wood species, such as fir and spruce.
It is standard practice in the lumber industry to dry or season several lumber pieces together for a certain period of time before these can be used or sold to customers. In a typical sawmill, once the wood has been cut to a specific length, the lumber pieces are put in a dryer. However, since not all lumber pieces have the same humidity level, some may be over-dried while others may remain too humid. Consequently, the quality of the lumber pieces becomes inferior as they are prone to twist, split or rot. One solution to this problem has been to sort or classify the lumber pieces according to their humidity level before the drying operation. An hygrometer is used to determine the humidity of each piece of wood. However, such classification does not yield satisfactory results because the measurement of humidity before the drying operation is not necessarily correlated with its drying time. For example, pieces of wood of different species may require different drying times even though their initial humidity levels are identical.
As seen above, there is a need to determine the drying time of a piece of wood in a simple and effective manner, which would lead to a more efficient sorting of the lumber pieces before the drying step.
Known in the art, Canadian Patent No. 1,326,908 (BEAUCHEMIN et al.) provides a method and an apparatus for detecting the humidity in cut lumber before sorting and drying the same. However, the apparatus uses weight sensors that are inadequate for precisely measuring the humidity level in the lumber pieces. Indeed, tests have shown that the weight of a piece of wood is not necessarily related to its humidity level. Furthermore, as mentioned above the determination of the humidity level in a piece of wood is not necessarily an indication of its drying time.
Also known in the art, Canadian Patent Application 2,270,274 (LEGER et al.) describes a method and an apparatus for facilitating the separation of lumber pieces that are of different species. The lumber pieces are coated with an indicator liquid and are optically scanned to identify their species prior to drying. The process is inefficient as it does not determine the drying time of a piece of wood and additionally requires the marking of each piece at an earlier step.
Also known in the art are U.S. Pat. Nos. 5,486,815 (WAGNER); 5,406,378 (JAMROZ et al.); 5,307,679 (ROSS); 5,317,274 (NAKAGAWA et al.); 4,876,889 (SHAKKOTTAI et al.); 4,683,418 (WAGNER et al.); 4,377,783 (WAGNER); 4,123,702 (KINANEN et al.); 4,059,988 (SHAW); 3,811,087 (SCHMELZER), which show various devices for measuring humidity of different materials or determining a species of a piece of wood, but are all unable to determine the drying time of a piece of wood in a simple and effective manner.
An object of the present invention is to provide a simpler and more effective apparatus and method for determining the drying time of a piece of wood and which does not suffer from the drawbacks of the prior art.
Another object of the invention is to provide a method and an apparatus for determining the drying time of a lumber piece, which is reliable and adapted to large scale sawmills, and can be used in a fully automated implementation.
According to the present invention, there is provided an apparatus for determining a drying time of a piece of wood, comprising:
a conveyor adapted to transport the piece of wood along a travelling path;
a probe mounted aside the travelling path, the probe having first and second electrodes extending next to one another and having spiked ends directed toward the travelling path for insertion into the piece of wood when the piece of wood transported by the conveyor passes by the probe, the second electrode having an input for receiving electric power, the first electrode having an output for transmission of a current signal having passed through the piece of wood from the second electrode to the first electrode;
driving means for selectively driving the probe toward and away from the piece of wood between a measuring position where the spiked ends of the electrodes are stuck in the piece of wood and a retracted position where the spiked ends of the electrodes are withdrawn from the piece of wood;
a control means connected to the driving means, for controlling operation thereof; and
a measuring means coupled to the outputs of the electrodes, for measuring the current signal, and determining the drying time of the piece of wood based on the current signal.
According to another aspect of the present invention, there is provided a method for determining a drying time of a piece of wood, using a probe having first and second electrodes extending next to one another and having spiked ends in a same direction, comprising the steps of:
transporting the piece of wood along a travelling path;
driving the probe against the piece of wood into a measuring position where the spiked ends of the electrodes are stuck in the piece of wood;
applying electric power on the second electrode while the spiked ends of the electrodes are in the measuring position;
measuring a current signal passing through the piece of wood from the second electrode to the first electrode;
removing the probe from the piece of wood into a retracted position where the spiked ends of the electrodes are withdrawn from the piece of wood when the current signal has been measured; and
determining the drying time of the piece of wood based on the current signal.
According to yet another aspect of the present invention, there is provided an apparatus for determining a drying time of a piece of wood, comprising:
a probe having first and second electrodes extending next to one another and having spiked ends directed in a same direction for insertion into the piece of wood, the second electrode having an input for receiving electric power, the first electrode having an output for transmission of a current signal having passed through the piece of wood from the second electrode to the first electrode; and
a measuring means coupled to the output of the first electrode, for measuring the current signal, and determining the drying time of the piece of wood based on the current signal.
According to still another aspect of the present invention, there is provided a method for determining a drying time of a piece of wood, using a probe having first and second electrodes extending next to one another and having spiked ends in a same direction, comprising the steps of:
driving the probe against the piece of wood into a measuring position where the spiked ends of the electrodes are stuck in the piece of wood;
applying electric power on the second electrode while the spiked ends of the electrodes are in the measuring position;
measuring a current signal passing through the piece of wood from the second electrode to the first electrode;
removing the probe from the piece of wood when the current signal has been measured; and
determining the drying time of the piece of wood based on the current signal.
The invention as well as its numerous advantages will be better understood by reading of the following non restrictive description of preferred embodiments made in reference to the appended drawings.